DRAFT Inventory of U.S Greenhouse Gas Emissions and Sinks

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Updating input variables that are from older data sources, such as beef births by month and beef cow lactation rates; Investigation of the availability of annual data for the DE, Y m, and crude protein values of specific diet and feed components for foraging and feedlot animals; Further investigation on additional sources or methodologies for estimating DE for dairy, given the many challenges in characterizing dairy diets; Further evaluation of the assumptions about weights and weight gains for beef cows, such that trends beyond 2007 are updated, rather than held constant; Further evaluation of the estimated weight for dairy cows (i.e., 1,500 lbs) that is based solely on Holstein cows as mature dairy cow weight is likely slightly overestimated, based on knowledge of the breeds of dairy cows in the United States; Potentially updating to a Tier 2 methodology for other animal types (i.e., sheep, swine, goats, horses); Investigation of methodologies and emission factors for including enteric fermentation emission estimates from poultry; Comparison of the current CEFM processing of animal population data to estimates developed using annual average populations to determine if the model could be simplified to use annual population data; and Recent changes that have been implemented to the CEFM warrant an assessment of the current uncertainty analysis; therefore, a revision of the quantitative uncertainty surrounding emission estimates from this source category will be initiated. 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 5.2 Manure Management (IPCC Source Category 3B) The treatment, storage, and transportation of livestock manure can produce anthropogenic CH 4 and N 2O emissions. Methane is produced by the anaerobic decomposition of manure. Nitrous oxide emissions are produced through both direct and indirect pathways. Direct N 2O emissions are produced as part of the nitrogen (N) cycle through the nitrification and denitrification of the organic N in livestock dung and urine. 3 There are two pathways for indirect N 2O emissions. The first is the result of the volatilization of N in manure (as NH 3 and NO x) and the subsequent + deposition of these gases and their products (NH 4 and NO - 3 ) onto soils and the surface of lakes and other waters. The second pathway is the runoff and leaching of N from manure to the groundwater below, in riparian zones receiving drain or runoff water, or in the ditches, streams, rivers, and estuaries into which the land drainage water eventually flows. When livestock or poultry manure are stored or treated in systems that promote anaerobic conditions (e.g., as a liquid/slurry in lagoons, ponds, tanks, or pits), the decomposition of the volatile solids component in the manure tends to produce CH 4. When manure is handled as a solid (e.g., in stacks or drylots) or deposited on pasture, range, or paddock lands, it tends to decompose aerobically and produce little or no CH 4. Ambient temperature, moisture, and manure storage or residency time affect the amount of CH 4 produced because they influence the growth of the bacteria responsible for CH 4 formation. For non-liquid-based manure systems, moist conditions (which are a function of rainfall and humidity) can promote CH 4 production. Manure composition, which varies by animal diet, growth rate, and type, including the animal’s digestive system, also affects the amount of CH 4 produced. In general, the greater the energy content of the feed, the greater the potential for CH 4 emissions. However, some higher-energy 3 Direct and indirect N2O emissions from dung and urine spread onto fields either directly as daily spread or after it is removed from manure management systems (i.e., lagoon, pit, etc.) and from livestock dung and urine deposited on pasture, range, or paddock lands are accounted for and discussed in the Agricultural Soil Management source category within the Agriculture sector. 5-8 DRAFTInventoryof U.S. GreenhouseGasEmissionsandSinks: 1990–2015

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 feeds also are more digestible than lower quality forages, which can result in less overall waste excreted from the animal. The production of direct N 2O emissions from livestock manure depends on the composition of the manure and urine, the type of bacteria involved in the process, and the amount of oxygen and liquid in the manure system. For direct N 2O emissions to occur, the manure must first be handled aerobically where ammonia (NH 3) or organic N is converted to nitrates and nitrites (nitrification), and then handled anaerobically where the nitrates and nitrites are reduced to dinitrogen gas (N 2), with intermediate production of N 2O and nitric oxide (NO) (denitrification) (Groffman et al. 2000). These emissions are most likely to occur in dry manure handling systems that have aerobic conditions, but that also contain pockets of anaerobic conditions due to saturation. A very small portion of the total N excreted is expected to convert to N 2O in the waste management system (WMS). Indirect N 2O emissions are produced when nitrogen is lost from the system through volatilization (as NH 3 or NO x) or through runoff and leaching. The vast majority of volatilization losses from these operations are NH 3. Although there are also some small losses of NO x, there are no quantified estimates available for use, so losses due to volatilization are only based on NH 3 loss factors. Runoff losses would be expected from operations that house animals or store manure in a manner that is exposed to weather. Runoff losses are also specific to the type of animal housed on the operation due to differences in manure characteristics. Little information is known about leaching from manure management systems as most research focuses on leaching from land application systems. Since leaching losses are expected to be minimal, leaching losses are coupled with runoff losses and the runoff/leaching estimate provided in this chapter does not account for any leaching losses. Estimates of CH 4 emissions from manure management in 2015 were 66.3 MMT CO 2 Eq. (2,651 kt); in 1990, emissions were 37.2 MMT CO 2 Eq. (1,486 kt). This represents a 78 percent increase in emissions from 1990. Emissions increased on average by 1.1 MMT CO 2 Eq. (3.0 percent) annually over this period. The majority of this increase is due to swine and dairy cow manure, where emissions increased 58 and 136 percent, respectively. From 2014 to 2015, there was a 5.4 percent increase in total CH 4 emissions from manure management, mainly due to an increase in larger farms and animal populations, as well a shifting of manure management to liquid systems with increasing farm size. Although the majority of managed manure in the United States is handled as a solid, producing little CH 4, the general trend in manure management, particularly for dairy and swine (which are both shifting towards larger facilities), is one of increasing use of liquid systems. Also, new regulations controlling the application of manure nutrients to land have shifted manure management practices at smaller dairies from daily spread systems to storage and management of the manure on site. Although national dairy animal populations have generally been decreasing since 1990, some states have seen increases in their dairy populations as the industry becomes more concentrated in certain areas of the country and the number of animals contained on each facility increases. These areas of concentration, such as California, New Mexico, and Idaho, tend to utilize more liquid-based systems to manage (flush or scrape) and store manure. Thus the shift toward larger dairy and swine facilities has translated into an increasing use of liquid manure management systems, which have higher potential CH 4 emissions than dry systems. This significant shift in both the dairy and swine industries was accounted for by incorporating state and WMSspecific CH 4 conversion factor (MCF) values in combination with the 1992, 1997, 2002, 2007 and 2012 farm-size distribution data reported in the Census of Agriculture (USDA 2016d). In 2015, total N 2O emissions from manure management were estimated to be 17.7 MMT CO 2 Eq. (59 kt); in 1990, emissions were 14.0 MMT CO 2 Eq. (47 kt). These values include both direct and indirect N 2O emissions from manure management. Nitrous oxide emissions have remained fairly steady since 1990. Small changes in N 2O emissions from individual animal groups exhibit the same trends as the animal group populations, with the overall net effect that N 2O emissions showed a 27 percent increase from 1990 to 2015 and a 1.1 percent increase from 2014 through 2015. Overall shifts toward liquid systems have driven down the emissions per unit of nitrogen excreted. Table 5-6 and Table 5-7 provide estimates of CH 4 and N 2O emissions from manure management by animal category. Table 5-6: CH4 and N2O Emissions from Manure Management (MMT CO2 Eq.) Gas/Animal Type 1990 2005 2011 2012 2013 2014 2015 CH4 a 37.2 56.3 63.0 65.6 63.3 62.9 66.3 Dairy Cattle 14.7 26.4 32.4 34.3 33.4 34.0 34.8 Agriculture 5-9